The work to date has shown the promise of impedance detection of bacterial growth. Major advantages over radioactive methods are safety, economy, and freedom from disposal problems. Impedance growth curves are characteristic and reproducible for many of the test strains. This finding was unexpected and warrants continued investigation. Impedance growth curves vary greatly between bacterial species. Brucella Abortus provides a very slow, steady millivolt response such that the computer does not signal the culture positive until the population density is 1x10 to the six bacteria/ml. Escherichia coli lowers impedance sufficiently at 1x10 to the four/ml to signal a positive culture. Since automation is the prime consideration at this time for using impedance detection, this large difference is not critical in early growth detection. Even a slow response usually prompts a positive signal long before visual detection would be likely.